1. Field of the Invention
The present invention relates to a cassette half and a tape cassette. More particularly, the present invention relates to a cassette half having a two-layer structure and a tape cassette formed by a pair of such cassette halves.
2. Background of the Invention
There is known a cassette for e.g. a sound recording and reproducing tape which includes a pair of cassette halves fitted together, and a pair of reel hubs which are enclosed between the cassette halves, and on which the tape can be wound. Each cassette half may have a two-layer structure as shown at 101 in FIG. 1, and include an inner resin layer 102 formed from a resin having a low modulus of elasticity, and an outer resin layer 103 formed from a resin having a high modulus of elasticity on the inner resin layer 102, as shown in FIGS. 1 to 3. The inner resin layer 102 improves the vibration-damping property of the cassette half.
The cassette half 101 is formed by injection molding the inner resin layer 102 in a mold, and the outer resin layer 103 on the outer surface of the inner resin layer 102. The outer resin layer 103 has a thin portion 104 lying on the inner resin layer 102, and a thick portion 105 contiguous to the thin portion 104, both as viewed across the thickness of the cassette half.
Each cassette half 101 has in the principal surface a pair of holes 107 through which the reel shafts, respectively, of a tape recording and/or reproducing apparatus can be inserted, as shown in FIG. 1. The two cassette halves 101 are joined together by screws, etc. to assemble a tape cassette 111, as shown in FIG. 1. Each cassette half 101 has in one of its edge surfaces a plurality of cuts which enable the cassette 111 to have a plurality of openings 108 through which the tape can be partly exposed, and into which the heads, pinch rollers, etc. of the recording and/or reproducing apparatus can be inserted. Reel hubs 109 and 110 partly project into the holes 107, respectively, and are rotatable by the reel shafts passed through the holes 107.
The outer resin layer 103 of each cassette half 101 has, however, an abrupt change in thickness between its thin and thick portions 104 and 105, as FIG. 2 shows that the thick portion 105 has an end surface 106 which is substantially perpendicular to the thin portion 104, or has an angle of about 90.degree. thereto. The shape of the outer resin layer 103 as described is apparently responsible for the problems which will be pointed out below:
(1) When the outer resin layer 103 hardens after injection molding, its shrinkage occurs to a greatly different degree between its thin and thick portions 104 and 105. The thick portion 105 undergoes much more shrinkage than the thin portion 104. As a result, the thick portion 105 becomes warped, as shown in FIG. 3, and the cassette half 101 is, therefore, deformed;
(2) The use of any cassette half 101 deformed by the warpage of its thick portion 105 has an adverse effect on the accuracy in thickness of the tape cassette 111; and
(3) The cassette 111 has a gap .delta. formed between the thick portions 105 of the cassette halves 101, as shown in FIG. 3. The gap .delta. is undesirable, since it is likely that dust, or the like may enter the cassette through the gap, or that a magnetic tape 112 may be caught in the gap, and thereby damaged.